Weeping in Blade Coating Part II: SEM and X-Ray Microanalysis of Microtome-Sectioned Weeps, 1993 Coating Conference Proceedings

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This is the second of two papers on visualization of the bleeding phenomenon in blade coating known as “weeping.” Here we report results of scanning electron microscopy (SEM) and x-ray microanalysis of air-dried, microtome-sectioned weeps. With few exceptions, the weeps all share a common structure: a bulbous crown atop a comb of separate columns or “trunks” that join, two-by-two, in their upper reaches. In some cases what evidently had been small droplets were seen attached to the legs, but there were not enough to support the mechanism of growth through droplet addition proposed by Gane et al. [2]. Cross-sectioned weeps showed excess numbers of calcium carbonate lumps and rafts of clay booklets, up to 36 /um across, in the trunks of the weeps, where they attached to the blade. This points to growth of the trunks-at least partly by blockage of large clay booklets and calcium carbonate lumps. The trunks were also less porous than the crowns, evidence that trunks and crowns grow by differcnt mechanisms.